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Dear Beth,<br>
<br>
From all my knowledge I gathered so far, I can try to answer your
question (and hope that people from this list correct me if I am
wrong):<br>
As often, the truth lies somewhere in between. The frequency
smoothing is determined by the type and length of the taper you
apply - this is similar to wavelet analysis. If you use multitapers,
you can specify cfg.tapsmofrq, which determines the frequency band
you want to smooth with. The FT freqanalysis method uses
multiplication in the time domain instead of convolution in the
frequency domain (which is equivalent). Any taper will always have a
specific frequency spectrum itself, and thus it will not give you
the value of a single frequency (though the output looks as if). So
if you specify foi as [5 10 15], then the power at 5Hz will not be
from 2.5 to 7.5Hz, but neither will it be at exactly and only 5Hz
(btw, the exact center frequency might not be 5Hz, this depends on
the (Rayleigh) frequency resolution of your signal).<br>
<br>
I do not know any more specifics concerning this, maybe the help of
ft_freqanalysis can tell you some additonal things:
<a class="moz-txt-link-freetext" href="http://fieldtrip.fcdonders.nl/reference/ft_freqanalysis">http://fieldtrip.fcdonders.nl/reference/ft_freqanalysis</a><br>
<br>
Best,<br>
Jörn<br>
<br>
Btw, if this is not correct, else from the mailinglist should
correct me asap ;)<br>
<br>
<br>
<br>
On 8/4/2011 3:23 PM, Belluscio, Beth (NIH/NINDS) [E] wrote:
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<p class="MsoNormal">Hi all-<o:p></o:p></p>
<p class="MsoNormal"> When calling ft_freqanalysis you specify
the foi limits and intervals – eg 5:5:30. The resulting data
set appears to generate the power at discreet frequencies (5,
10, 15, 20, 25, 30). Does this actually reflect an estimate
of the power over a range of frequencies (2.5-7.5, 7.5-12.5,
12.5-17.5,….) or the power at discreet frequencies with those
in between not evaluated? <o:p></o:p></p>
<p class="MsoNormal"> Thanks for your help,<o:p></o:p></p>
<p class="MsoNormal">Beth.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Beth Belluscio MD-PhD<o:p></o:p></p>
<p class="MsoNormal">Clinical Fellow<o:p></o:p></p>
<p class="MsoNormal">Human Motor Control Section<o:p></o:p></p>
<p class="MsoNormal">NINDS, NIH<o:p></o:p></p>
<p class="MsoNormal">301-402-3495<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<pre wrap="">_______________________________________________
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<br>
<br>
<pre class="moz-signature" cols="72">--
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands
Contact:
E-Mail: <a class="moz-txt-link-abbreviated" href="mailto:jm.horschig@donders.ru.nl">jm.horschig@donders.ru.nl</a>
Tel: +31-(0)24-36-68493
Web: <a class="moz-txt-link-freetext" href="http://www.ru.nl/donders">http://www.ru.nl/donders</a>
Visiting address:
Trigon, room 2.30
Kapittelweg 29
NL-6525 EN Nijmegen
The Netherlands</pre>
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